The present invention relates to polyurethane compositions, in particular a humidity curing one-component polyurethane composition comprising a prepolymer which, besides of isocyanate groups, also comprises latent amino groups bonded to the prepolymer. The polyurethane composition can e.g. be used as filling composition for any kind of joints, as adhesive for elastic bonding or as elastic coating for sealing areas.
One-component polyurethane compositions comprising latent amines are known for a long time and broadly described. In comparison with usual one-component polyurethane compositions, that are cured by the reaction with ambient humidity, the compositions comprising latent amines have the advantage that upon curing by means of said latent amines no CO.sub.2 is liberated and thus no blisters are formed.
GB 1,064,841 and EP 469,751 for example describe one-component polyurethanes that besides isocyanate groups comprising prepolymers comprise polyaldimines as latent amines.
The known systems, however, show the following disadvantages:
In order to cure, they need a relatively high amount of water. In order to add two moles of prepolymer chains, two moles water are needed. Two aldimine groups of a polyaldimin have to be hydrolyzed, so that each of the two liberated amino groups then can make an addition reaction with one isocyanate group of a polymer chain and accordingly two moles of aldehyde are liberated. These systems of the state of the art have therefore the disadvantage that they are slowly curing in places deep under the surface, since a relatively high amount of water has to diffuse through the already formed skin. Also for the application in thick layers, as they are often found in the case of sealing joints and elastic bonding, a fast through-curing of the whole layer is desired. Furthermore, the aldehyde formed during curing in quite large amounts can affect the features of the material.
EP 19 906 describes one-component polyurethane systems that, besides isocyanate groups comprising prepolymers, also comprise latent amines, namely polyurethanes comprising cycloaminals as latent amines. The cycloaminals are produced from a diamine with two secondary amino groups and an aldehyde. As substituents at the C-atoms of the ring hydrogen and alkyl groups are mentioned. Said systems only need one mole water for liberating the two secondary amino groups and thus for the addition of two isocyanate comprising prepolymer chains, and furthermore also only one mole of aldehyde is liberated. The use of secondary amines as curing agents in the polyurethane chemistry, however, has the disadvantages that the formation of hydrogen bonds between the ureas of the polymer chains are hindered due to the formed N-substituted ureas, thereby affecting the features of the material.
EP 1 065 describes one-component polyurethanes that comprise cycloaminals as latent amines whereby the cycloaminals are bonded to the isocyanate groups comprising prepolymer by means of urea groups. For the production of said cycloaminals amines with a secondary and a primary amino group are used.
According to EP 19 906 as well as EP 1 065, for the production of the cycloaminals preferably aldehydes are used, that lead to products with an insufficient storage stability, in particular in combination with the cheap aromatic isocyanates. Furthermore, these aldehydes, upon curing of the products, lead to an intense smell that is a great nuisance, in particular for the application on large areas and/or for the use of the polyurethane compositions in the interior of buildings.